Here is a photo of my NRG Pro5 TX prototype. Im hoping to have this in
production very soon.

This new version uses an at frequency oscillator so there is no ½ and 1½
frequency harmonics to deal with and gives a very clean output, however on
the other hand its susceptible to hum and RF feedback. The oscillator
*must* be shielded from the rest of the board and especially from the power
supply (not shown in this version), grounding and bypassing at RF is also
very important.

This prototype gives 5 watts across the entire band and uses a 2SC1971 for
the output. Tuning is done by holding in the up/down push buttons for 3
seconds then setting your frequency, there is no requirement to manually
tune a trimmer capacitor and watch for lock output. The oscillator uses two
varicaps, one for tuning and one for modulation. There is a hex 4049
inverter which generates 30v to drive the tuning varicap, this allows for a
wide tuning range and better stability with less noise. Ignore the red wire
in bottom right corner of pcb, I forgot to run one of the traces to correct
location.

The PLL is a TSA5511 and is controlled over i2c using a pic 16F628A. The
TSA5511 RF pickup is inductively coupled to the end of the oscillator coil.
Charge pump current is increased during the tuning/locking stage, then
reduced once locked for a very stable output and very little chance of the
PLL trying to "correct" the base frequencies down at 30hz.

No pre-emphasis is included with this design as there should *always* be
some form of deviation control before the transmitter and this should be
doing the pre-emphasis.

Gareth

Ross Levis

Can the power output be adjustable? This is required to be legal depending on the antenna gain and coax loss etc. From: LPFM_Radio@yahoogroups.com.au

Message 2 of 3
, 26 Mar

Can the power output be adjustable? This is required to be legal depending on the antenna gain and coax loss etc.

Here is a photo of my NRG Pro5 TX prototype. I’m hoping to have this inproduction very soon.

This new version uses an “at frequency” oscillator so there is no ½ and 1½frequency harmonics to deal with and gives a very clean output, however onthe other hand its susceptible to hum and RF feedback. The oscillator*must* be shielded from the rest of the board and especially from the powersupply (not shown in this version), grounding and bypassing at RF is alsovery important.

This prototype gives 5 watts across the entire band and uses a 2SC1971 forthe output. Tuning is done by holding in the up/down push buttons for 3seconds then setting your frequency, there is no requirement to manuallytune a trimmer capacitor and watch for lock output. The oscillator uses twovaricaps, one for tuning and one for modulation. There is a hex 4049inverter which generates 30v to drive the tuning varicap, this allows for awide tuning range and better stability with less noise. Ignore the red wirein bottom right corner of pcb, I forgot to run one of the traces to correctlocation.

The PLL is a TSA5511 and is controlled over i2c using a pic 16F628A. TheTSA5511 RF pickup is inductively coupled to the end of the oscillator coil.Charge pump current is increased during the tuning/locking stage, thenreduced once locked for a very stable output and very little chance of thePLL trying to "correct" the base frequencies down at 30hz.

No pre-emphasis is included with this design as there should *always* besome form of deviation control before the transmitter and this should bedoing the pre-emphasis.

Gareth

Gareth Parker

I have thought about that, and at this stage IÆm planning to vary the supply to the final two transistors hopefully without running into saturation problems

Message 3 of 3
, 26 Mar

I have thought about that, and at this stage I’m planning to vary the supply to the final two transistors hopefully without running into saturation problems in the driver stage. The other option is to release two versions of this board with different matching in the output stages.

I am still debugging the pic code also, I wrote this in hi-tech c using mplab. Step size is 50khz, however for lpfm use I’m considering programming the pic to only allow selection of lpfm frequencies. There will also be the option of a hard coded frequency which will allow removal of the lcd panel from the main pcb. This may be useful for technical people who setup other stations but don’t want their customers tampering with gear etc… I know I’ve had a few of those, one guy I setup kept jumping across frequencies causing problems for everyone else.

Here is a photo of my NRG Pro5 TX prototype. I’m hoping to have this inproduction very soon.

This new version uses an “at frequency” oscillator so there is no ½ and 1½frequency harmonics to deal with and gives a very clean output, however onthe other hand its susceptible to hum and RF feedback. The oscillator*must* be shielded from the rest of the board and especially from the powersupply (not shown in this version), grounding and bypassing at RF is alsovery important.

This prototype gives 5 watts across the entire band and uses a 2SC1971 forthe output. Tuning is done by holding in the up/down push buttons for 3seconds then setting your frequency, there is no requirement to manuallytune a trimmer capacitor and watch for lock output. The oscillator uses twovaricaps, one for tuning and one for modulation. There is a hex 4049inverter which generates 30v to drive the tuning varicap, this allows for awide tuning range and better stability with less noise. Ignore the red wirein bottom right corner of pcb, I forgot to run one of the traces to correctlocation.

The PLL is a TSA5511 and is controlled over i2c using a pic 16F628A. TheTSA5511 RF pickup is inductively coupled to the end of the oscillator coil.Charge pump current is increased during the tuning/locking stage, thenreduced once locked for a very stable output and very little chance of thePLL trying to "correct" the base frequencies down at 30hz.

No pre-emphasis is included with this design as there should *always* besome form of deviation control before the transmitter and this should bedoing the pre-emphasis.

Gareth

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